The invention relates to a high frequency power supply device that feeds high frequency power to a load such as a plasma processing device.
As disclosed in Patent Document 1, a high frequency power supply device has been known which has a rectification smoothing circuit that converts a commercial alternating current voltage into a direct current voltage, a DC-DC converter that converts the direct current voltage obtained from the rectification smoothing circuit into an alternating current voltage and again converts the alternating current voltage into a direct current voltage and an inverter circuit that converts an output of the DC-DC converter into high frequency alternating current power and which controls an output voltage of the DC-DC converter, thereby approximating high frequency power to be fed to a load to a setting value.
FIG. 8 shows a configuration of the high frequency power supply device disclosed in Patent Document 1. In FIG. 8, a reference numeral 1 denotes a rectification smoothing circuit that rectifies an alternating current voltage obtained from a commercial power supply into a direct current voltage and smoothes the same, a reference numeral 2 denotes a DC-DC converter to which the direct current voltage obtained from the rectification smoothing circuit is input and a reference numeral 3 denotes an inverter circuit that an output of the DC-DC converter 2 into high frequency alternating current power.
As shown in FIG. 9, the inverter circuit 3 is a well-known circuit that has a switch circuit having switch elements S1 to S4, which are H-bridged, and feedback diodes D1 to D4, which are respectively inverse-parallel connected to the switch elements S1 to S4. The inverter circuit 3 alternately turns on the switch elements S1, S4, which configure a pair of one opposite sides of the H bridge, and the switch elements S2, S3, which configure the other pair of the other opposite sides, thereby converting the direct current voltage Vdc applied from the DC-DC converter 2 into a high frequency alternating current voltage Vinv having a rectangular waveform.
The high frequency alternating current voltage having a rectangular waveform, which is output from the inverter circuit 3, is converted into high frequency voltage and current of sinusoidal waveforms and then supplied to a load 7. In the shown example, the output of the inverter circuit is input to a primary side of a transformer 4 and an output of the transformer 4 is input the load 7 through a series resonance circuit 5 and a lowpass filter 6. The alternating current voltage and current having rectangular waveforms, which are output by the inverter circuit 3, are converted into the high frequency voltage and current of sinusoidal waveforms by the series resonance circuit 5 and the lowpass filter 6 and are then supplied to the load 7.
A reference numeral 8 denotes a voltage detection unit that detects the output voltage of the inverter circuit 3, a reference numeral 9 denotes a current detection unit that detects the output current linv of the inverter flowing between the inverter circuit 3 and the transformer 4, and a reference numeral 10 denotes a power detection unit that detects the high frequency power to be fed to the load 7.
An output of the voltage detection unit 8 and an output of the current detection unit 9 are input to a phase difference detection unit 11 that detects a phase difference of the output current of the inverter circuit 3 with respect to the output voltage and a detection value of the phase difference obtained from the phase difference detection unit 11 is applied to a frequency control unit 12′ that generates a frequency instruction for determining an output frequency of the inverter circuit 3.
A reference numeral 13 denotes a high frequency signal generation unit that generates a high frequency signal of a sinusoidal waveform having a frequency instructed by the frequency instruction applied from the frequency control unit 12′, a reference numeral 14 denotes a signal conversion unit that converts the high frequency signal output from the high frequency signal generation unit 13 into control signals V1, V2 to be applied to the switch elements of the inverter circuit 3 and a reference numeral 15 denotes a power control unit that performs control of approximating a power value of the high frequency power to be fed from the inverter circuit to the load to a setting value or maintaining the power value within a set allowable range.
The control signal V1 is a control signal that is applied to the control terminals of the switch elements S1, S4, which configure the pair of one opposite sides (sides of diagonal positions) of the H bridge configuring the inverter circuit 3, so as to turn on the switch elements S1, S4, and the control signal V2 is a control signal that is applied to the control terminals of the switch elements S2, S3, which configure the pair of the other opposite sides of the H bridge configuring the inverter circuit 3, so as to turn on the switch elements S2, S3. The high frequency signal generation unit 13 is comprised of a direct digital synthesizer (DDS) that generates a sinusoidal wave signal having a frequency as instructed by the applied frequency instruction.
In the high frequency power supply device disclosed in Patent Document 1, the output frequency of the inverter circuit 3 is controlled so that the phase difference of the high frequency alternating current and high frequency voltage, which are applied to the load, is small (preferably, zero) to the extent possible. When the output frequency of the inverter circuit is controlled as described above, a switching loss that occurs in the switch elements configuring the inverter circuit 3 can be reduced to improve the efficiency of the high frequency power supply device.
In a high frequency power supply device that feeds high frequency power to a load such as plasma processing device, it is necessary to maintain the high frequency power, which is applied to the load, at a setting value. In the high frequency power supply device shown in FIG. 8, it is necessary to perform the control of maintaining the high frequency power, which is applied from the inverter circuit 3 to the load through the transformer 4, the series resonance circuit 5 and the lowpass filter 6, at a setting value. Therefore, in the high frequency power supply device of the above type, although not particularly described in Patent Document 1, the output voltage of the DC-DC converter 2 that generates the direct current power to be input to the inverter circuit 3 is controlled to control the high frequency power that is fed to the load 7. In the example shown in FIG. 8, the output of the power detection unit 10 is applied to the power control unit 15. The power control unit 15 calculates a deviation between the detection value of the high frequency power, which is applied to the load 7, and the setting value and controls the value of the output voltage of the DC-DC converter 2 so that the calculated deviation approximates to zero (0). Thereby, the output voltage and output current of the inverter circuit 3 are controlled to keep the high frequency alternating current power, which is applied to the load 7, at the setting value.
In the example shown in FIG. 8, the rectification smoothing circuit 1 and the DC-DC converter 2 configure a direct current power supply unit. Also, the phase difference detection unit 11, the frequency control unit 12′, the high frequency signal generation unit 13 and the signal conversion unit 14 configure an inverter control unit 25′, and the inverter circuit 3, the transformer 4, the series resonance circuit 5, a filter unit 6, the voltage detection unit 8, the current detection unit 9 and the inverter control unit 25′ configure a high frequency power generation unit PS′. Also, the direct current power supply unit configured by the rectification smoothing circuit 1 and the DC-DC converter 2, the high frequency power generation unit PS′, the power detection unit 10 and the power control unit 15 configure the high frequency power supply device.
Patent Document 1: JP-A-2007-185000 (FIG. 4)
In the high frequency power supply device shown in FIG. 8, in order to perform the control of keeping the high frequency power to be applied to the load at the setting value, the DC-DC converter 2 capable of controlling the direct current output voltage is provided at a front stage of the inverter circuit 3 and the output voltage of the DC-DC converter 2 is controlled so that the power detected by the power detection unit 10 is kept at the setting value. Therefore, the configuration of the power supply device is complicated and the cost thereof is high.
Also, the DC-DC converter has a high-capacity smoothing capacitor therein, so that it takes to lower the output voltage thereof. Thus, the control responsiveness gets worse. In order to enhance the control responsiveness, it is necessary to provide a circuit that forcibly discharges the smoothing capacitor of the DC-DC converter, for example. Thereby, the circuit configuration is complicated.
Also, in FIG. 8, it may be considered that the DC-DC converter 2 is omitted and the switch elements of the inverter circuit 3 are PWM-controlled to keep the power, which is fed to the load 7, at the setting value. However, in order to PWM-control the switch elements of the inverter circuit 3, it is necessary to turn on/off the switch elements with a frequency remarkably higher than the output frequency of the inverter circuit 3. Therefore, when the output frequency of the inverter circuit 3 is high (for example, several 10 MHz to several 100 MHz for performance of the current switch element), it is difficult to adopt the above consideration.